1. Field of the Invention
The present invention relates to a heat pump type airconditioner in which a heat source in a warming mode is a heater.
2. Description of the Prior Art
In general, heat pump type airconditioners employing an ambient air heat source have numerous merits, e.g. they are safe, the energy utilization efficiency is high and cooling and warming can be performed with an identical machine. This system, however, involves such essential disadvantages that when the temperature of the outdoor air falls, the warming capability deteriorates to a point such that the desired warming is impossible, and that various troubles attributed to frost on the parts of the apparatus occur. Airconditioners in which a combustor for kerosene, town gas or the like is incorporated in the unit with a cooling device are free from the disadvantages of the aforementioned heat pump type apparatus employing an ambient air heat source, but they have the disadvantage that the initial cost is high.
As a cooling and warming apparatus making the best use of the features of both the types of airconditioners, there has recently been proposed a system in which, in a cooling mode, a refrigerant is circulated in order through a compressor--an outdoor heat exchanger--a pressure reducing device--an indoor heat exchanger--and the compressor so as to perform cooling, while in a warming mode, the refrigerant is circulated in order through the compressor--the indoor heat exchanger--an outdoor side heater provided with a heating mechanism--and the compressor so as to perform warming (as, for example, U.S. patent application Ser. No. 362,838, filed Mar. 29, 1982 in the name of Tamotsu Nomaguchi et al, corresponding to Japanese Patent Application No. 55-137408, by Mitsubishi Denki Kabusiki Kaisha).
FIG. 1 shows a prior-art refrigeration circuit in a heat pump type airconditioner provided with a refrigerant heating mechanism. In the cooling mode, a refrigerant delivered from a compressor 1 is led by a four-way transfer valve 2 to an outdoor heat exchanger 3 where the refrigerant is condensed. After passing through a check valve 5, the liquid refrigerant has its pressure reduced by a throttle mechanism 7, and it is evaporated by an indoor heat exchanger 9 so as to cool a room. The flow of the refrigerant is controlled by the four-way transfer valve 2 again so as to bring the refrigerant back to the compressor 1.
In the warming mode, the refrigerant circulation circuit is changed-over by the four-way transfer valve 2 as follows. First, the refrigerant at a high temperature is condensed by the indoor heat exchanger 9, giving up heat to the room, and the liquid refrigerant is passed through a check valve 8 of a bypass circuit which is connected in parallel with the throttle mechanism 7. Then the refrigerant is circulated through a check valve 6 to a refrigerant heating heat exchanger 4, being blocked by the action of the check valve 5 disposed on the downstream side of the outdoor heat exchanger 3. After the refrigerant is heated and evaporated in the heat exchanger 4, it passes through the four-way valve and returns to the compressor again.
In addition, there is provided a compressor bypass circuit 10 which is provided with a solenoid valve 11 and which connects the delivery side and suction side of the compressor 1. The bypass circuit 10 functions as follows. In the cooling mode, when the cooling load is small, the valve 11 is opened to divert refrigerant from the main circuit so that energy-converting airconditioning can be carried out during which the cooling capability is kept low so that the electric power input to the compressor can be reduced. In the warming mode, specifically at the beginning thereof, the valve 11 is kept open until the circulation state or circulation rate, the temperature, etc. of the refrigerant which is heated by the refrigerant heating heat exchanger employing a combustor of town gas, kerosene or the like reaches a predetermined stable state. In another aspect of use, for the same purpose as in the cooling mode, when the warming load is small, the valve 11 is opened, and the thermal input to the refrigerant heating mechanism is simultaneously reduced, whereby the warming capability is adjusted.
However, when employing an external heat source such as a burner which is at a temperature higher than that of the ambient air, heat is radiated into the lower temperature ambient air by the heat exchanger in the above described prior art system, and the heating efficiency deteriorates. Therefore, a method has been considered in which, in the warming mode, the heat exchanger in the prior art apparatus is filled up with the refrigerant in its liquid phase so as to reduce the heat radiation to the utmost. With this method, however, the quantity of the refrigerant within the circuit becomes too large, resulting in the disadvantage that in the cooling mode the compressor is difficult to start when beginning the cooling mode.
In case of the prior-art refrigeration circuit provided with the refrigerant heating mechanism as shown in FIG. 1, when the refrigerant heating is initiated simultaneously with the starting of the compressor at the beginning of the warming, the operating state becomes as shown in FIG. 2. The temperature of the ambient air is low in the warming condition. Therefore, at the time t.sub.1 at which the warming is begun, the refrigerant accumulates in the outdoor part of the refrigeration circuit, particularly the refrigerant heating mechanism and the outdoor heat exchanger. Immediately after the starting, accordingly, the circulation rate of the refrigerant is very great, and liquid compression is liable to occur. Moreover, a long time passes before a steady state is reached.
Besides, in the refrigerant heating mechanism, a steady heating capability is provided at the same time as the initiation of its operation at a time t.sub.o ', so that the temperature of the refrigerant on the suction side of the compressor becomes very high. This is prone to adversely affect the refrigerant, refrigerating machine oil in the circuit, and the compressor. More particularly, in the refrigerant heating mechanism which employs the combustion heat of town gas, kerosene or the like as the refrigerant heating source, the adjustment of the combustion capability is difficult, and hence the aforementioned disadvantage is conspicuous. When the temperature of the refrigerant on the suction side of the compressor has reached a predetermined upper limit at a time t.sub.3, the refrigerant heating is stopped, and the operation of the compressor is continued. When the suction side temperature has fallen to a predetermined point at a time t.sub.4, the refrigerant heating is initiated again. After such steps have been repeated several times, there is established the state in which the refrigerant temperature does not reach the upper limit requiring the stopping of the refrigerant heating, so a stable operation can then be obtained.
With the above method, however, the ON/OFF operations of the heater, such as the burner, are repeated many times until the stable state is established. Therefore, the method needs a long time for producing a warm temperature in the room, and it cannot compensate for the disadvantage of an insufficient warming capability at a low temperature of the ambient air unless the conventional heat pump type airconditioner is provided with the refrigerant heating mechanism. Moreover, disadvantages exist related to misfire of the burner as well as safety and to the life of the equipment.
With the heat pump type airconditioner of this sort, when a compressor having the required capability for the cooling mode is installed, the refrigerant bypasses the throttle mechanism during the warming mode. During the steady operation, therefore, the circulation rate of the refrigerant is much larger than in the cooling mode, and the warming capability becomes too high. Moreover, since the frequent repetition of the ON/OFF operations of the combustor is attended with difficulty, the solenoid valve is normally kept open so as to bypass the refrigerant therethrough. The effect of preventing the liquid compression of the refrigerant at the beginning of the operation is also expected from the opening of the bypass valve. In spite of the foregoing step, however, the airconditioner of this sort has, even in the warming mode, the disadvantage of the frequent repetition of the ON/OFF operations of the combustor and the inferior warming effect on the room.